Method and apparatus for diagnosing a malfunction of a clutch actuator

ABSTRACT

In a method and apparatus for diagnosing a malfunction in a clutch actuator of a motor vehicle, the actual position of the clutch actuator is measured by a position sensor. Simultaneously, an estimated position of the clutch actuator is calculated by an emulation unit that emulates the function of the clutch actuator. Malfunctions of the clutch-actuator are diagnosed by comparing the actual, measured position to the estimated position.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a method and apparatus fordiagnosing a malfunction in a clutch actuator of a motor vehicle. Theclutch actuator receives an input command signal of variable magnitudefrom a control unit that may belong to an automatically shiftingtransmission, an automated clutch or a continuously variabletransmission. The input command signal controls the position of theclutch actuator and thereby sets the state of engagement of the clutch.As a common trait of the inventive method as well as existing methods,the clutch-actuator position or state of engagement of the clutch ismeasured and an output signal corresponding to the measured actuatorposition is made available.

[0002] In the search for safety-monitoring concepts for automaticallyshifting transmissions, it has been found that many critical situationsarise mainly in connection with the actuation of the clutch, e.g., ifthe clutch moves into or out of engagement at times when this is notintended. It is therefore of the highest importance to have real-timeinformation about the current status of the clutch.

[0003] In connection with automatic or automated clutches ortransmissions, it is a known concept to provide a measurement signalthat indicates the position of the clutch actuator. However, as a matterof principle, the possibility of failure has to be taken into accountfor a position-sensor of the clutch actuator just as for any othertechnical component. Thus, the position of the clutch actuator asindicated by the sensor is not unconditionally reliable. Consequently,in connection with monitoring the safety of automated shifttransmissions, it is highly advisable to include the clutch position orclutch actuator position in the monitoring process.

[0004] As an attempt to satisfy this need, a known concept of monitoringthe position sensor of the clutch actuator involves a plausibility testbased on minimum and maximum signal values. However, this allows onlycertain extreme malfunctions of the sensor to be discovered, e.g., ashort circuit or a break in the cable.

OBJECT OF THE INVENTION

[0005] The present invention therefore has the objective of providing amethod of diagnosing malfunctions in a clutch actuator, whereby theposition of the clutch actuator and the state of engagement of theclutch can be monitored with a higher degree of reliability incomparison to known state-of-the-art methods.

[0006] The invention further has the objective of providing an apparatusin the form of a clutch-actuating system in which the safe functioningof the clutch is assured in accordance with the inventive method.

SUMMARY OF THE INVENTION

[0007] The objective outlined above is met by the method according tothe invention, as follows: The clutch actuator receives an input commandsignal of variable magnitude from a control unit that may belong to anautomatically shifting transmission, an automated clutch or acontinuously variable transmission. The input command signal controlsthe position of the clutch actuator and thereby sets the state ofengagement of the clutch. The clutch-actuator position or state ofengagement of the clutch is measured, and a position signalcorresponding to the actually measured actuator position is madeavailable. The method according to the invention is distinguished inthat the aforementioned input command signal is simultaneously appliedto the input of an emulation model of the actuator. The emulation modelcalculates a signal representing a theoretically estimated actuatorposition. The respective signals for the actual and theoretical actuatorpositions are compared to each other in a comparator unit which sendsthe result of the comparison to an arithmetic unit. The arithmetic unit,in turn, generates a status signal that characterizes the degree offunctionality of the clutch actuator.

[0008] The object of the invention is further met by a variation of theinventive method, wherein, the position signal corresponding to themeasured actuator position is entered as an input into a processor unitfor the function of the clutch and the dynamic behavior of the engine,which generates an rpm-signal representing the actually measuredrpm-rate of the engine. The position signal corresponding to themeasured actuator position is simultaneously entered as an input into acalculator unit, which generates a theoretical rpm-signal representing atheoretically estimated rpm-rate of the engine based on the positionsignal and the engine torque. The respective signals for the actuallymeasured and theoretically estimated rpm-rate are compared to each otherin a comparator unit which produces a comparison signal that isindicative of the functionality of the clutch actuator.

[0009] The objective stated above is also accomplished by a furthervariation of a method for diagnosing a malfunction of a clutch, with thefollowing elements: A first electrical signal generated by a firstsensor indicates if the motor vehicle is standing still. A secondelectrical signal generated by a second sensor indicates if a gear inthe automatically shifting transmission cannot be synchronized within aprescribed time interval. A third electrical signal generated by a thirdsensor indicates if the engine is running. The first, second and thirdelectrical signals are brought together and evaluated in a logicAND-member which sets an error flag indicating a malfunction in theclutch-actuating system if all three signals are affirmative.

[0010] As a further contribution to meet the above objective, theinvention provides an apparatus in the form of a clutch-actuating systemwherein the actuation of a clutch is automated and the safe functioningof the clutch is assured through the method according to the inventionas described herein, including its different embodiments and variations.

[0011] The method according to the present invention has the principaladvantage that it offers a far-reaching degree of detection ofmalfunctions of a clutch actuator in a relatively simple way bycorrelating the actual position of the clutch actuator as measured by asensor with a theoretically estimated actuator position provided by anemulation model of an actuator as a function of the position-controllinginput command signal.

[0012] The novel features that are considered as characteristic of theinvention are set forth in particular in the appended claims. Theimproved apparatus itself, however, both as to its construction and itsmode of operation, together with additional features and advantagesthereof, will be best understood upon perusal of the following detaileddescription of certain presently preferred specific embodiments withreference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Preferred embodiments of the invention will be described below indetail based on the attached drawings, wherein

[0014]FIG. 1 represents a block diagram of a first embodiment of theinvention;

[0015]FIG. 2 represents a block diagram of a second embodiment of theinvention;

[0016]FIG. 3 represents a block diagram of a third embodiment of theinvention; and

[0017]FIG. 4 represents a further developed embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0018]FIG. 1 shows a clutch actuator 1 and an emulation model 2 of theclutch actuator 1. The emulation model calculates the position that theactuator should theoretically occupy based on a current value of aposition-controlling input command signal that is simultaneously fed tothe input 10 of the clutch actuator 1 and the input 20 of the emulationmodel 2. The position-controlling input command signal is generated byan automatically shifting transmission. The clutch actuator 1 moves toor occupies a position that is a function of the position-controllinginput command signal. The actual position of the clutch actuator 1 ateach point in time is measured by a sensor and made available as anelectrical output signal (representing the actually measured actuatorposition) at an output 11 of the clutch actuator 1.

[0019] Based on the position-controlling input command signal that issimultaneously fed to the input 20 of the emulation model 2, the lattercalculates a position value of a position that the clutch actuatorshould theoretically occupy based on the current value of theposition-controlling input command signal. The theoretical positionvalue is presented at the output 21 of the emulation model 2. Therespective signals at the outputs 11 and 21 for the actually measuredactuator position and the theoretically estimated actuator position arebrought together in a comparator unit 3, e.g., a summation stage, wherethey are compared to each other. The comparator unit 3 delivers theresult of the comparison (in the form of a comparison signal at output31) to an arithmetic unit 4 which, in turn, generates a status signal atoutput 41. If the respective signals for the actually measured andtheoretically calculated actuator position approximately agree with eachother, the arithmetic unit will find, based on an evaluation algorithm,that both the clutch actuator and the position sensor of the clutchactuator are functioning properly. On the other hand, if there is alarge discrepancy between the respective signals for the actuallymeasured and theoretically calculated actuator position, the arithmeticunit will determine that there is a malfunction in the clutch actuatorand/or the position sensor of the clutch actuator 1.

[0020] To compensate for the fact that the actually measured andtheoretically estimated signal values would drift apart over time as aresult normal friction wear on the clutch, it is recommended to returnthe comparison signal from the comparator unit 3 through a feedback line24 to the input 22 of the emulation model 2, so that the normal amountof drifting-apart can be taken into account in calculating thetheoretically estimated signal value.

[0021] The block diagram of FIG. 2 illustrates an embodiment of theinvention where the method steps of FIG. 1 are followed by additionalmethod steps, in which the result of a clutch actuator position ormovement is evaluated, i.e., the magnitude or change of the torque thatis transmitted by the clutch. The elements in FIG. 2 that correspond toanalogous elements in FIG. 1 have the same reference symbols.

[0022] The position signal at the output 11 of the clutch actuator 1,which represents the actually measured actuator position, is also fed tothe input 50 of a processor unit 5 that for the function of the clutchand the dynamic behavior of the engine, which delivers at its output 51a signal determined by a sensor, representing the actually measuredrpm-rate of the engine. The signal from output 51 is sent to the input60 of a further comparator unit 6.

[0023] Analogously, the signal at the output 21 of the emulation model2, which represents the theoretically estimated actuator position, isalso fed to the input 70 of a calculator unit 7, which calculates atheoretical rpm-rate of the engine based on the theoretically estimatedactuator position and the engine torque. The theoretical rpm-signal issent from the output 71 of the calculator unit 7 to an input 62 of thefurther comparator unit 6, e.g., a summation stage, in which the signalsfrom outputs 51 and 71 are compared to each other. The comparator unit 6delivers a comparison result (Res 2) from its output 61 to an arithmeticunit (not shown). The comparison result Res 2, which represents thedifference between the actually measured rpm-rate and the theoreticallycalculated rpm-rate of the engine, is evaluated by the arithmetic unitand used as an indicator for the condition of the clutch. The comparisonsignal Res1 at the output 31 of the comparator unit 3 is evaluated bythe arithmetic unit 4 (described above in the context of FIG. 1) as anindicator for the condition of the clutch actuator.

[0024] Thus, the embodiment of FIG. 2 offers additional detectioncapabilities for malfunctions. For example, if the position sensor ofthe clutch actuator fails during a start-up phase or a gear-shift phase,the failure will manifest itself within a very short time through alarge value of the comparison signal Res 1 at the output 31 of thecomparator unit 3, while the comparison signal Res 2 at the output 61 ofthe comparator unit 6 remains small, because the clutch actuator 1 isstill setting the clutch correctly to the targeted position. If on theother hand the clutch actuator 1 itself is defective, both of thecomparison signals (i.e., Res1 at output 31 and Res2 at 11 output 61)will increase rapidly. It is further symptomatic of a malfunction of theclutch or clutch actuator if the comparison signal Res 1 at output 31 ofthe comparator unit 3 remains small, while the comparison signal Res 2at output 61 of the comparator unit 6 shows large values.

[0025] The added possibility of detecting not only the presence but alsothe location of a malfunction offers considerable advantages in regardto the safety or fitness for use of a vehicle with an automated shifttransmission. To compensate for a drifting-apart of the signals for theactually measured and theoretically estimated engine rpm-rate, theoutput signal Res2 can be returned from the comparator unit 6 through afeedback line 64 to the calculator unit 7, so that a normal amount ofdrifting-apart can be taken into account in calculating thetheoretically estimated signal value.

[0026]FIG. 3 illustrates a simplified embodiment in which the functionof monitoring the clutch actuator has been left out. Those details inFIG. 3 that have already been described in the context of FIG. 2 areidentified with the same reference symbols. The embodiment of FIG. 3does not have the emulation model 2 nor the comparator unit 3.Accordingly, the position-sensor signal representing the measuredposition of the clutch actuator is applied to the input 50 of theprocessor unit 5 and simultaneously to the input 70 of the calculatorunit 7. A signal representing the actually measured engine rpm-rate isdelivered from output 51 of the processor unit 5 to input 60 of thecomparator unit 6; and a signal representing a theoretically estimatedengine rpm-rate is delivered from output 71 of the calculator unit 7 toinput 62 of the comparator unit 6. The signals from outputs 51 and 71are compared to each other in the comparator unit 6, which delivers acomparison result (Res 2) representing the difference between theactually measured rpm-rate and the theoretically calculated rpm-rate ofthe engine. The comparison result Res2 is used as an indicator fordetecting malfunctions of the clutch or the clutch actuator system.

[0027] An embodiment of the inventive method according to FIG. 4 servesto detect a particular type of malfunction of the clutch actuator or ofthe clutch itself, where the clutch does not, or not completely,disengage so that the transmission of torque through the clutch is neverinterrupted. Consequently, it will not be possible to put thetransmission in gear, even when the engine is running. If thetransmission is forcibly shifted into gear too often, this can causedamage to the synchronization.

[0028]FIG. 4 represents in block-diagram form an engine 100 transmittinga torque through a clutch 300 to the transmission 200 which, in turn,drives the wheels 500.

[0029] Three sensors, S1, S2, S3 are used to detect a situation wheretorque is transmitted continuously from the engine 100 to thetransmission 200 by way of the clutch 300. Sensor S1 emits an electricalsignal that indicates if the vehicle is standing still; sensor S3 emitsan electrical signal that indicates if the engine is running; and sensorS2 emits an electrical signal that indicates if a gear that has been setin the automatically shifting transmission cannot be synchronized withina prescribed time interval. The signals of the sensors S1, S2, S3 arebrought together and evaluated in a logic AND-member 400. If all threesignals are affirmative, the logic device 400 sets an error flag Findicating that the clutch actuator is malfunctioning in the mannerdescribed above. In response to the error flag F, the transmission 200is shifted into neutral.

[0030] Preferably, the error flag F is canceled if the driver indicatesan intent to shift into first gear by using the selector lever of thetransmission 200 before a prescribed time limit has elapsed.

[0031] The method of FIG. 4 provides an advantageous way of detectingthe following malfunctions and preventing their potential consequences:

[0032] 1. An undesirable condition where the clutch 200 transmits torquewhile the vehicle is standing still can be detected and/or avoided.

[0033] 2. A defective hydraulic system or an incorrect startingprocedure of a driver can be recognized.

[0034] 3. A defect in the transmission actuator can be detected.

[0035] 4. If the wheel rpm-rate sensor has failed and thereforeindicates zero rpm, it is possible to detect inappropriate attempts toshift the transmission into first gear.

[0036] Without further analysis, the foregoing will so full reveal thegist of the present invention that others can, by applying currentknowledge, readily adapt it for various applications without omittingfeatures that, from the standpoint of prior art, fairly constituteessential characteristics of the generic and specific aspects of theabove outlined contribution to the art of motor vehicles and controllingthe rpm-rates of its prime mover and, therefore, such adaptations shouldand are intended to be comprehended within the meaning and range ofequivalence of the appended claims.

What is claimed is:
 1. A method of diagnosing a malfunction of a clutchactuator that actuates the engagement and disengagement of a clutch of amotor vehicle with a transmission and a control unit, comprising thesteps of: a) feeding an input command signal representing a desiredamount of clutch engagement from the control unit to the clutch actuatorand simultaneously feeding the input command signal to an emulationmodel of the clutch-actuator; b) measuring the clutch-actuator positionand generating an actual position signal corresponding to the measuredclutch-actuator position; c) calculating in the emulation model atheoretically estimated clutch-actuator position based on the inputcommand signal, and generating an estimated position signalcorresponding to the theoretically estimated clutch-actuator position;d) feeding the actual position signal and the estimated position signalto a first comparator unit which, in turn, generates a first comparisonsignal representing the result of a comparison of said actual andestimated position signals; e) feeding the first comparison signal to afirst arithmetic unit which evaluates the first comparison signal and,based on said evaluation, generates a first status signal that ischaracteristic of the clutch-actuator's ability to function properly. 2.The method of claim 1 wherein, if the first comparison signal indicatesthat the actual position signal and the estimated position signal agreewith each other within a first prescribed limit, the first status signalwill indicate that both the clutch actuator and the position sensor ofthe clutch actuator are functioning properly.
 3. The method of claim 1,wherein if the first comparison signal indicates that a discrepancybetween the actual position signal and the estimated position signalexceeds a prescribed limit, the first status signal will indicate thatthere is a malfunction in at least one of the clutch actuator and theposition sensor of the clutch actuator.
 4. The method of claim 1,wherein the first comparison signal is returned from the firstcomparator unit through a first feedback line to the emulation model, sothat the emulation model can apply a correction to keep the actualposition signal and the estimated position signal from drifting apart.5. The method of claim 1, further comprising the steps of: f) feedingthe actual position signal to a processor unit for the function of theclutch and the dynamic behavior of the engine, which generates an actualrpm signal based on an rpm-sensor input, representing a measuredrpm-rate of the engine; g) feeding the estimated position signal to acalculator unit which calculates a theoretically estimated enginerpm-rate based on the estimated position signal and a current enginetorque and generates an estimated rpm signal representing thetheoretically estimated engine rpm-rate; h) feeding the actual rpmsignal and the estimated rpm signal to a second comparator unit which,in turn, generates a second comparison signal representing the result ofa comparison of said actual and estimated rpm signals; i) feeding thesecond comparison signal to a second arithmetic unit which evaluates thesecond comparison signal.
 6. The method of claim 5 wherein, if thesecond comparison signal indicates that the actual rpm signal and theestimated rpm signal agree with each other within a second prescribedlimit, the second arithmetic unit will generate a second status signalindicating that the clutch actuator is functioning properly.
 7. Themethod of claim 6 wherein, if the second status signal indicates thatthe clutch actuator is functioning properly and at the same time thefirst comparison signal indicates that a discrepancy between the actualposition signal and the estimated position signal exceeds a prescribedlimit, the conclusion is made that the clutch actuator is functioningproperly and that the position sensor of the clutch-actuator has amalfunction.
 8. The method of claim 5, wherein, if the first comparisonsignal indicates that a discrepancy between the actual position signaland the estimated position signal exceeds a first prescribed limit andthe second comparison signal indicates that a discrepancy between theactual rpm signal and the estimated rpm signal exceeds a secondprescribed limit, the conclusion is made that the clutch actuator has amalfunction.
 9. The method of claim 5, wherein, if the first comparisonsignal indicates that the actual position signal and the estimatedposition signal agree with each other within a first prescribed limit,while the second comparison signal indicates that a discrepancy betweenthe actual rpm signal and the estimated rpm signal exceeds a secondprescribed limit, the conclusion is made that there is a malfunction inat least one of the clutch, the clutch actuator, and an engine rpmsensor.
 10. The method of claim 5, wherein the second comparison signalis returned from the second comparator unit through a second feedbackline to the calculator unit, so that the calculator unit can apply acorrection to keep the actual rpm signal and the estimated rpm signalfrom drifting apart.
 11. A method of diagnosing a malfunction of aclutch actuator that actuates the engagement and disengagement of aclutch of a motor vehicle with a transmission and a control unit,comprising the steps of: a) feeding an input command signal representinga desired amount of clutch engagement from the control unit to theclutch actuator; b) measuring the clutch-actuator position andgenerating an actual position signal corresponding to the actuallymeasured clutch-actuator position; c) feeding the actual position signalto a processor unit for the function of the clutch and the dynamicbehavior of the engine, which generates an actual rpm signal based on anrpm-sensor input, representing a measured engine rpm-rate; d)simultaneously with step c), feeding the actual position signal to acalculator unit which calculates a theoretically estimated enginerpm-rate based on the estimated position signal and a current enginetorque and generates an estimated rpm signal representing thetheoretically estimated engine rpm-rate; e) feeding the actual rpmsignal and the estimated rpm signal to a comparator unit which, in turn,generates a comparison signal representing the result of a comparison ofactual and estimated rpm signals; f) based on said comparison signal,making a conclusion about the condition of the clutch.
 12. The method ofclaim 11, wherein the comparison signal is returned from the comparatorunit through a feedback line to the calculator unit, so that thecalculator unit can apply a correction to keep the actual rpm signal andthe estimated rpm signal from drifting apart.
 13. A method of diagnosinga malfunction of a clutch of a motor vehicle with a transmission,comprising the steps of: a) by means of a first sensor, generating afirst electrical signal, which indicates if the motor vehicle isstanding still; b) by means of a second sensor, generating a secondelectrical signal, which indicates if a gear in the automaticallyshifting transmission cannot be synchronized within a prescribed timeinterval; c) by means of a third sensor, generating a third electricalsignal, which indicates if the engine is running; d) evaluating thefirst, second and third electrical signals in a logic AND-member whichsets an error flag indicating a malfunction in the clutch-actuator ifall three signals are affirmative.
 14. The method of claim 13, whereinthe transmission is shifted into neutral when the error flag has beenset.
 15. The transmission of claim 13, wherein the error flag iscanceled if a selector lever of the transmission is actuated by a driverof the motor vehicle before a prescribed time limit has elapsed afterthe error flag has been set.
 16. An apparatus for automaticallyactuating a clutch with a clutch actuator, wherein the apparatus isadapted to perform the method of claim
 1. 17. An apparatus forautomatically actuating a clutch with a clutch actuator, wherein theapparatus is adapted to perform the method of claim
 11. 18. An apparatusfor automatically actuating a clutch with a clutch actuator, wherein theapparatus is adapted to perform the method of claim 13.